In a digital communications system, a transmitter transmits digital data in the form of signals to a receiver over one or more communication links. The aforementioned Cassiday patent application describes a digital communications system in which information signals are transmitted from the transmitter to the receiver along with a clocking signal, which serves to synchronize the transfer of the information signals therebetween. In that system, the information is transferred at high speed on both the leading and trailing edges of the clocking signal, which creates a number of problems. First, so that the transmitter circuit can transmit the information at high speed, it will be necessary minimize the propagation delay, and the differences in propagation delay, from the transmitter's circuits in which the information is stored, to the circuits which select and drive the signals onto the links interconnecting the transmitter and receiver. This is a particular problem in connection with digital communications systems for use in modern digital systems, which typically include testing circuitry for performing a number of types of tests to determine whether the system is operating correctly, and, if not, which portion(s) of the system is (are) operating incorrectly. Typically, such testing circuitry adds circuitry to the transmitter and receiver which can increase the propagation delay problems and may require reduction in the rate of information transmission from the transmitter to the receiver.